A concise, flexible, and efficient total synthesis of the cytotoxic resin glycosides ipomoeassin B (1) and ipomoeassin E (2) is reported which features the advantages of a novel protecting group strategy employing (Z)-3-dimethyl(phenyl)silyl-2-propenoic acid as cinnamic acid surrogate. The use of this readily available compound allowed the macrocycle of the glycolipids to be formed by ring closing olefin metathesis (RCM) with the aid of the second generation Grubbs carbene complex 12. The resulting E/Z mixture could be selectively hydrogenated using Wilkinson's catalyst [RhCl(PPh3)(3)] without affecting the unsaturated esters in the periphery of the compound, before the C-silyl group was cleaved off with TASF [tris(dimethylamino)sulfonium difluorotrimethylsilicate] under notably mild conditions to release the required cinnamate moiety. Other key steps of the synthesis route comprise the formation of the disaccharide linkage by the trichloroacetimidate method, the formation of the chiral acid segment 19 via a VO(acac)(2)-catalyzed, tert-BuOOH-induced oxidative rearrangement of the optically pure furyl alcohol (-)-15 (Achmatowicz-type reaction), and a reductive cleavage of the 4,6-O-p-methoxybenzylidene acetal in 5 with NaBH3CN and Me3SiCl (TMSCl), the regiochemical course of which was found to be opposite to that previously reported in the literature for sterically less encumbered substrates.
Copper-Catalyzed Enantiotopic-Group-Selective Allylation of <i>gem</i>-Diborylalkanes
作者:Minjae Kim、Bohyun Park、Minkyeong Shin、Suyeon Kim、Junghoon Kim、Mu-Hyun Baik、Seung Hwan Cho
DOI:10.1021/jacs.0c11750
日期:2021.1.20
We report a copper-catalyzed enatiotopic-group-selective allylation of gem-diborylalkanes with allyl bromides. The combination of copper(I) bromide and H8-BINOL derived phosphoramidite ligand proved to be the most effective catalytic system to provide various enantioenriched homoallylic boronate esters, containing a boron-substituted stereogenic center that is solely derived from gem-diborylalkanes
acid represents the key design element of a totalsynthesis of all known members of the ipomoeassin family of resin glyosides. This protecting group maneuver allows the unsaturated acids decorating the glucose subunit of the targets to be attached at an early phase of the synthesis, prevents their participation in the ruthenium‐catalyzed ring‐closing metathesis (RCM) used to form the macrocyclic ring,
Chiral Synthesis via Organoboranes. 47. Efficient Synthesis of Unsymmetrical Ketones and Enantiomerically Pure Spiroketals Using (±)-Isopinocampheyldichloroborane
作者:Herbert C. Brown、Shekhar V. Kulkarni、Uday S. Racherla、Ulhas P. Dhokte
DOI:10.1021/jo980989w
日期:1998.10.1
intermediate was readily converted into the unsymmetrical ketones, R(1)COR(2), in high yields and purity, by an established method. This methodology was successfully applied to the synthesis of enantiomerically pure spiroketals using optically pure TBS ether protected homoallylic alcohols as the alkenes for stepwise hydroboration.
Stereoselective Synthesis of the Macrolactone Core of (+)-Neopeltolide
作者:Sadagopan Raghavan、Pradip Kumar Samanta
DOI:10.1021/ol3007698
日期:2012.5.4
A stereoselectivesynthesis of the macrolactonecore of the potent anticancer agent neopeltolide is disclosed. The key steps of the synthesis include asymmetric allylation using Krische’ protocol, conjugate reduction using MacMillan’s methodology, and an asymmetric hetero-Diels–Alder reaction using Jacobsen’s catalyst. Substrate controlled diastereoselective 1,3-anti reduction of a keto alcohol, Luche
Gold(I)-Catalyzed Cyclization for the Synthesis of 8-Hydroxy-3- substituted Isocoumarins: Total Synthesis of Exserolide F
作者:N. Arjunreddy Mallampudi、G. Sudhakar Reddy、Saurabh Maity、Debendra K. Mohapatra
DOI:10.1021/acs.orglett.7b00673
日期:2017.4.21
regioselective gold(I)-catalyzed 6-endo-dig cyclization of 2,2-dimethyl-5-(alkynyl)-4H-benzo[d][1,3]dioxin-4-ones for the synthesis of 8-hydroxy-3-substituted isocoumarins is described. Key features of the reaction include the broad substrate scope, scalability, and tolerance for protecting groups. The synthetic utility of this novel method is demonstrated by the first total synthesis of exserolide
高度区域选择性的金(I)催化2,2-二甲基-5-(炔基)-4 H-苯并[ d ] [1,3]二恶英-4-酮的6-内挖环化反应合成8描述了-羟基-3-取代的异香豆素。该反应的关键特征包括广泛的底物范围,可扩展性和对保护基的耐受性。这种新方法的合成实用性是由Exserolide F(一种含异香豆素的多元醇天然产物)的第一次全合成证明的。